The present invention relates to the general field of turbomachine blades of composite material comprising fiber reinforcement densified by a matrix.
The intended field is that of rotors having composite material blades for aeroengines or for industrial turbines.
Proposals have already been made to use composite material for making turbomachine blades. By way of example, reference may be made to patent application FR 08 58090 (not yet published) filed in the joint names of Snecma and Snecma Propulsion Solide, describing the fabrication of a turbomachine blade by making a fiber preform by three-dimensional weaving and densifying the preform with a matrix.
For a rotor having metal blades, the rotor generally has a plurality of metal blades mounted via their roots on a metal disk, together with a metal casing placed around the rotor. During assembly (when cold) of the rotor inside the casing, it is necessary to leave radial clearance between the tips of the blades and the casing that surrounds the rotor. However, in operation (when hot), this clearance can give rise to leaks of gas between the tips of the blades and the casing.
In order to reduce the risk of such leaks appearing, the free ends of the blades are generally provided with radial labyrinth teeth, and an abradable material is mounted on the inside surface of the casing facing the labyrinth teeth. In operation of the rotor, the disks, the blades, and the casing surrounding the rotor all expand in such a manner that the labyrinth teeth carried by the blades abrade the abradable material carried by the casing. As a result, the clearance left on assembly between the tips of the blades and the casing tends to disappear, thereby limiting gas leakage.
In contrast, with a rotor having blades made of composite material, the expansion differences between the rotor (made in part out of the composite material of its blades) and the casing (made of metal) can become large. As a result, when operating hot, the radial clearance left during assembly between the labyrinth teeth of the blades and the abradable material of the casing does not disappear completely, thereby having the consequence of sealing between the rotor and the casing no longer being fully ensured.